Metal V-belts such as this have been known for some time, and are disclosed, for example, in Japanese Utility Model Laid-Open No. 62-131143, Japanese Patent Laid-Open No. 2-225840, and Japanese Patent Laid-Open No. 7-12177. These metal V-belts used in the past comprise an endless belt-form ring member and numerous metal element members (also called metal links)supported along this ring, and are looped between a drive pulley and a driven pulley so as to transmit power. These two pulleys are designed so that the width of the V-groove thereof can be varied, and are designed so that the loop radius of the V-belt can be varied and the gear ratio continuously varied by varying this V-groove width.
When power is transmitted between the two pulleys by a metal V-belt such as this, the metal element members are pushed upon while the power is transmitted, so that the power is transmitted by the compression force acting on the metal element members. At this time a tensile force acts on the metal ring member that ties the numerous metal element members together in a ring, flexural stress acts [on this metal ring member] while [the V-belt] is looped around the two pulleys, and frictional force acts on the portion in contact with the metal element members.
It is therefore necessary to take into account these various forces that act on the ring member, and to optimize the material, shape, and so on thereof so that the strength and service life will be satisfactory with respect to these forces. Here, the ring member generally comprises a plurality of superposed, thin, endless belt-form metal ring sheets, and since the innermost and outermost ring sheets are in contact with the metal element members, they are subjected to frictional force and are prone to wear, making the durability of the innermost and outermost ring sheets the most frequently encountered problem.